This is an attempt to make a blog in which I comment on scientific issues.

Wednesday, July 22, 2009

Chimpanzees get AIDS too

This is really more the area of Tara or ERV but I still thought I'd comment on this piece of news.

African primates can be infected with over 40 different simian immunodeficiency viruses (SIVs). These diseases are related to two diseases which infects our particular species of primates, Homo sapiens, human immunodeficiency virus types 1 and 2 (HIV-1 and HIV-2) - indeed the two types of HIV are the result of SIVs crossing the species barrier.

HIV is considered an epidemic with more than 30 million people suffering from it worldwide (source - .pdf). As people hopefully know, HIV 1 and 2 will, if not treated by medicine, result in acquired immune deficiency syndrome (AIDS), which is fatal. 2 million people died from AIDS in 2007.

HIV and AIDS is one of the top prioritized areas of medical studies, and both the evolution of HIV from SIV and the connection between HIV and AIDS are well understood. This doesn't, however, keep some people from either claiming that HIV/AIDS is man-made, or that AIDS doesn't exist.

One of the arguments used by both groups is that SIV doesn't lead to AIDS in primates - the one group to argue that HIV couldn't have evolved from SIV, the other to argue that AIDS is not real.

Neither group makes sense. The lack of development of AIDS in SIV carrying primates is by no means evidence of there being no SIV-HIV connection, nor evidence of there being no HIV-AIDS connection.

Still, this matters even less now. Researchers have found out that some primates can get AIDS.

African primates are naturally infected with over 40 different simian immunodeficiency viruses (SIVs), two of which have crossed the species barrier and generated human immunodeficiency virus types 1 and 2 (HIV-1 and HIV-2)1, 2. Unlike the human viruses, however, SIVs do not generally cause acquired immunodeficiency syndrome (AIDS) in their natural hosts3. Here we show that SIVcpz, the immediate precursor of HIV-1, is pathogenic in free-ranging chimpanzees. By following 94 members of two habituated chimpanzee communities in Gombe National Park, Tanzania, for over 9 years, we found a 10- to 16-fold higher age-corrected death hazard for SIVcpz-infected (n = 17) compared to uninfected (n = 77) chimpanzees. We also found that SIVcpz-infected females were less likely to give birth and had a higher infant mortality rate than uninfected females. Immunohistochemistry and in situ hybridization of post-mortem spleen and lymph node samples from three infected and two uninfected chimpanzees revealed significant CD4+ T-cell depletion in all infected individuals, with evidence of high viral replication and extensive follicular dendritic cell virus trapping in one of them. One female, who died within 3 years of acquiring SIVcpz, had histopathological findings consistent with end-stage AIDS. These results indicate that SIVcpz, like HIV-1, is associated with progressive CD4+ T-cell loss, lymphatic tissue destruction and premature death. These findings challenge the prevailing view that all natural SIV infections are non-pathogenic and suggest that SIVcpz has a substantial negative impact on the health, reproduction and lifespan of chimpanzees in the wild.

In other words, there is a non-trivial health cost in being infected with SIVcpz.

The results suggest that it will not be possible to find the key to HIV immunity in the chimpanzee genome, as scientists had hoped. However, the study, published in Nature, sets the stage for researchers to gain insight into how HIV and SIV cause disease in their hosts by studying the responses of different primates to the viruses. Wild monkeys that have coexisted with SIV for a long time — such as sooty mangabeys and African green monkeys — seem to have evolved the ability to control SIV, and so do not become ill when exposed to the virus. The new paper, however, shows that chimpanzees — which, like humans, were exposed to SIV more recently — are sickened by the virus.